Occurrence and potential human-health significance of synthetic organic contaminants in sources of drinking water

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Robert J. Gilliom, rgilliom@usgs.gov, John S. Zogorski, Gregory C. Delzer, Michael J. Focazio, and Patricia L. Toccalino. U.S. Geological Survey, Placer Hall, 6000 J Street, Sacramento, CA 95819
Assessments of more than 300 organic contaminants in U.S. streams and ground water indicate:(1) most streams that have significant agricultural or urban land in their watersheds have multiple contaminants present most of the time; (2) contaminants are less frequent, but not rare, in ground water; (3) only a small proportion of contaminants that have human-health benchmarks exceeded a benchmark in any sample and in only a small proportion of source waters; (4) there probably are many additional contaminants present that have not yet been detected; and (5) mixtures of multiple contaminants are more common than individual contaminants. Inadequate toxicity data for many contaminants, the high frequency of complex mixtures, the unknowns about the human-health effects of mixtures, and the varying effectiveness of treatment technologies result in uncertainty about the human-health significance of organic contaminants in sources of drinking water and indicate key areas where research is needed.